Here's a plot idea I made up in accordance with what you have in mind:

After the catalysmic war fought against the evil armies of the darkness sent to the face of the earth to cleanse and destroy all that is living and turn the continent into an empire of undead to serve the fulfillment of the evil lord's higher destiny,  everyone that is left; people, nobility, magicians and the priests of the Land are in need of an extraordinary power that will serve their purpose in search of freedom and a world free of eternal darkness.  The wisdom of the ancients, the verses of the holy scripture, the prophecies of the oracles and the legends of the common folk speak of a man who will appear in the hardest of times from the heart of the Land and will bring order, peace and prosperity to chaos. But all is written, told or heard is not fact but fiction and there is no brave hero around. Heavy is the head that wears the crown: Heir to the throne, the one and only son of the king who was killed in the cataclysmic war, sets out to find the said hero. On his quest for the hero that will save the Land, he journeys to four corners of the Land, from the merciless deserts and miraculous mirages of the South to the frozen and barren steppes of North, from green and merry land of East to the cavernous cities of the West. Each of his destionations has its own secrets within. And as the prince wanders the land he encounters many tribes, towns, cities and landscapes and he experiences many things; slaughtered kins, mad sorcerers, doomsday preachers, corrupted traitor priests, remanants of the evil armies of darkness and whatnot. As he ends each feud and solves each problem his reputation as a hero than a prince grows wider and his quest for the legendary hero becomes a quest for his inner hero. One by one, he brings peace to each land and collects each of the four artifacts of the ancients. By the time he returns to the capital he finds the land invaded by the evil army. Equipped with the ancient artifacts he fights the enemy and saves his land, people and fulfills his destiny written thousands of years ago both in holy scripture and tales etc. He is the awaited hero.

I know it sounds very generic with the phrases such as "evil armies of darkness" etc but a name can be given each of these also backstories to deepen and expand the lore of the game.

So basicly game consists of Five Chapters. And maybe an prologue. Each of them explores a part of the continent/kingdom/land, contains many side quests in addition to the main quest.

Prologue: set in the heart of the land, (capital of the kingdom which is also the largest city on continent) The protagonist starts his quest to seek the hero. This is the main quest of the game, but the underlying quest is rather internal and personal than a worldly one, it is set in the vein of Monomyth, a.k.a. The Hero's Journey: http://upload.wikimedia.org/wikipedia/commons/1/1b/Heroesjourney.svg

First Chapter: Hero travels to the west of the Land. Goes into many caverns, underground towns, (a fallen, ancient city?) or even dungeons. Protagonist learns that there's more than meets the eye. Fights the White Tiger who protects one of the artifacts of the ancients.

Second Chapter: After defeating the legendary creature, his transformation to a hero already began. He has his doubts about the ancient legends speaking of a saviour but on the other hand he continues his quest nevertheless. He, then travels to North, to the land of Ice, where frozen steppes lies unbound. In this unexplored land, he meets tribes new to him, learns new ways of living and whatnot. A local legend speaks of a black tortoise in the Ice Temple of the Old, which keeps the sacred relic.

Third Chapter: His path now leads to the Great Forest of the East, full of scary creatures, swamps and poisonous ivy. There he meets many of the legendary creatures told in fairy tales. He now believes what he heard before but still has strong doubts about the One. In the end he defeats the Blue Dragon which reveals him the path to the hero he's seeking for.

Fourth Chapter: With the knowledge he gained from the Blue Dragon he leads to the Desert of the South, devoid of all life save for evil spirits and the fortress of the evil powers. This is a kind of a netherworld for the protagonist where he descends, "dies" and is reborn as the awaited hero. (This is clearly symbolized by the Phoenix he's to defeat in this chapter.) But he's still not fully aware that he's the hero he's looking for.

Epilogue: After his transformation, the hero turns back to his homeland just to find it under invasion of the evil lords. Now a hero, he clears his palace of the evil powers thus saves the capital, land and therefore world.  Probably he kills the gold dragon, (he becomes the new sun.)

Actually the protagonist's journey is just a reflection of the change of seasons; (Fall>Winter>Spring>Summer) thus it can be considered as the path of the Sun. (His quest roughly takes one year to complete.) So, in a way he is related to the sun, thus is one of the many interpretations of the Sun-God myth. (Check The Golden Bough by J. Frazer for reference) Thus, it makes it easier to enrich it with mythical symbols and expand the lore of the game.

Here's a quick sketch to visualize the plot idea I suggested. (Click to enlarge)

The Cyclic journey of the protagonist over the continent also symbolizes the round shape of the Sun in the sky and its orbit over the course of seasons. At the end of the game, the hero returns to capital  as the Sun and his people are enlightened by his wisdom and let live by the light of his heroic deeds.

Open world games are always preferable in a fantasy setting as exploring gives strange satisfaction, besides roaming the land may offer deeper knowledge of the backstory (talking to people etc) and more sidequests.  Also the open world enables the addition of other towns/places than the Four Corners of the Land according to the Wu Xing. More things to explore, learn, experience and of course loot.

Here's a little elaboration upon my suggested plotline. Names of characters and places are just random, used for demonstration purposes only.The map is incomplete but it'll give you some suggestions. The largest landpiece is Ahra, where our "capital" is located. To its northwest lies the Isle of Boorkh and east of Boorkh is the Frozen Steppes. The south of Ahra lies the Great Desert of the South; Al-Khari.

Map of Ahra and Surrounding Islands

Background

The year is 567, five and forty years after the last battle of the Ahra Wars; Battle of the Crimson Cradle, fought between the evil armies of the Eastern Principalities led by the Uthalian Lords and the Khaanite Kingdom of the Northwest. War leaves Ahra continent devastated, cities lie crumbled, counties barren, wasted and palaces burning. Remnants of the unholy creatures summoned from the unknown planes and raised undead armies from the fallen fellow comrades by the Uthalian Lords hide amongst the darker places of Ahra; at ruins, inside dumb wells, beneath the cryptic underground labyrinths, in the corridors of the unseen dungeons of Boorkh and even on the icy summits of the Mount Fhurr. These abominations haunt the land, killing sheep, cattle, humans and all the hope for prosperity in the northwestern kingdom. Nobles, merchants, sorcerers, priests and the common folk seek haven from these creatures of evil descent. They turn to their capital, heart of the Khaanite Kingdom and their king as a last resort. Ancient tales speak of a saviour that will rise from the heart of Ahra. Some say that he, Dhunar the King is that hero but he knows well that he is not. To find the legendary hero, to save his people and his land, (and to find out who he really is) he sets out.
 

The Capital, West Marshes and the Isle of Boorkh (Prologue & Chapter I)

Advised by the elders of the palace and guided by the high priests of the temple he sets out where the sun sets, to raise it once again over the face of Ahra. With this faith in his heart, his great-grand father’s sword by his side and holy relics of his creed upon his neck, undercover, he travels west of the kingdom, to the West Marshes where many unknown spirits dwell amongst the few towns and villages of his subjects.
 
Possible plot developments are:

• The Capital & Outer City: mostly interacting with NPCs & taking quests, reading about game lore, also vendors
• Wilderness: some creatures to be slain in the open wilderness, maybe some ruins of the destroyed former capital, even catacombs
• West Marshes: some spirit creatures, possible side quests (set some tormented soul free, fetch some soulstone for the priest in the capital, kill the dæmons haunting the village etc)
• Port Wetrock: small-scale quests to enable sailing to the Isle of Boorkh aboard. collecting items/raw materials for merchants. possible vendors. game lore learned from the sailors and travellers. Also, serve as a henchmen for local guardsmen to defend the port against creatures.
• Boorkh: the isle at the northwest of Ahra. Mountainous region with harsh climate. Rich in raw materials. (iron, and other fantastical ores; suitable for upgrading/forging of weaponary and armor) abandoned mines, a web of underground caverns, some long-forgotten creatures dwelling in the mines, something uncanny is hidden at the far end of the mines; it is the reason that the mining stopped.Some big boss to kill, probably.
• Land of the Boorkhish Tribes: a medium-scale village hidden inside a valley. vendors. side quests; collecting some magical ore from unexplored mines, saving the cheiftain from other tribe. Tribe wisdom learned. (i.e. game lore about the White Tiger living on top of the Borak Mountains=quest) climbing to the Borak Mountains, killing everything on the way,
• White Tiger’s Lair: a natural, carved temple, many levels to explore with the White Tiger at the end to kill.
• Boorkh Plains to the east of the island lie the plains. Uninhabited lands except for wild creatures and some Boorkish tribes. a couple of small-scale side quests on the plains, thus obtaining a ticket to cross the sea to the next chapter. Or a really huge bridge is already there. he just clears the way for the Boorkish tribes of the plain.

Frozen Steppes and Mount Fhurr (Chapter II)

As Dhunar (the protagonist) journeys to the Frozen Steppes with what he learned from his previous journeys, his quest goes on. Aided by the Boorkish plain tribes he travels to the Frozen Steppes, the small island north of Ahra. He is welcomed on the shores as he re-opened the route/bridge between the Frozen Steppes and Boorkish Plains.

Possible plot developments are:

• Frozen Steppes Shore: He’s welcomed by a small group of settlers; The Frost People. These people are in dire distress as they have not much natural resources to survive. taking quest of cleansing the steppes of the abysmal creatures, so that Frost People can hunt, cut trees to build ships for cruising again. kills the monster in the hills that raids the settlement and eats the livestock. Game lore: learns of the ice caverns with powerful crystals.
• Ice caverns: explore caves. Kill frost giants. Acquires powerful crystal.
• Wilderness: ancient ziggurats with deformed architecture lies here, a hidden city to explore. Full of wolves and other nightly (and even winged sea creatures?) creatures.
• Explore the mystery of the powerful crystal over the steppes. Stonehenge-like ancient temple and the catacombs underlying. (Game Lore learned from the ancient stone tablets etc.)
• Defeat the soul-devouring monster in the ancient catacombs. Learn that he produces the crystal. It is one of the sources of the Uthlian Lords used for raising the dead.
• Climb the Ice Temple of the old on Mount Fhurr to find the mythical Black Tortoise.

I'll post some more later on. Let me know what you think.

Neverwinter Nights also has a very nice story. Something like that could be done. They started with a problem (the plague), the city was seeking heroes to solve it, the most promising ones were allowed in the acedemy, and the opponent attacked the acedemy, killing most of the heroes, except the main character. First the problems in the city are to be solved, and then the goal is to seek the roots of the evil, and destroy them.

Neverwinter Nights also has a very nice story. Something like that could be done. They started with a problem (the plague), the city was seeking heroes to solve it, the most promising ones were allowed in the acedemy, and the opponent attacked the acedemy, killing most of the heroes, except the main character. First the problems in the city are to be solved, and then the goal is to seek the roots of the evil, and destroy them.

I have not read all the plot suggestions but the "we won Great war against the evil army, but now they are back" is cliche as it comes.

I think that this sounds better.

The world has been is a time of great learning, deep knowledge, and plenty for countless ages.  The having all they could want or need all but a few have come to living the most beautiful Mega-Cities to enjoy their lives. Magic and Science or is it Science and Magic? It doesn't matter it's all the same to the living Mass of the people who can't tell them apart. But the age is shifting once more will the dominance of man over the world continue? All the while these long ages other forces in the world have been growing. Will anyone bare the burden needed for man to continue remain on top?

"I don't want to use the "hero of prophecy" hook or the King/prince/noble hook for the main hero."

good point ! i have saved to many worlds...

To be more iconoclast it should be interresting to have no main quest at all, only plenty of quests, some verry long and other more short.The character can choose which one he wants to follow depending of his mood.With all these quests you can have a overall view of a original world whitout following a path, you explore a world without changing it.

At my point of view this would be a real role playing game.

It's just an idea...

Then the moders can add some quests whithout bothering to match with a main quest and it makes a virtually neverending story ! I really like the concept of Morrowind (even if it had a "prophecy hook" main quest) with the fantastic editor and what the community have done (and continue to do) with adding content .

sorry for my english...

Here's a rough story idea based on the Wu Xing worldbelief where one element conquers another.

You start in the central city themed around metal. You get a metal artifact and are sent on a quest to wood lands. By defeating the wood guardian, you get a wood artifact. Your journey then leads you to underground, to earth domain. There you defeat the earth guardian and get the earth artifact. This artifact is needed to conquer the water sphere. Once you do that, you get the water artifact and can now take on the fire realm. Once you defeat the fire guardian you get the fire artifact. Your last task is to go to the metal city and defeat the metal guardian, thus completing the circle. Guardians and artifacts are different parts of the same whole, this is why you don't yet finish once you have all five artifacts and have to do that last level in the metal city. Once you complete all tasks, the whole universe transcends in perfection and a new cycle of existence starts.

This is the rough framework and of course you fill the in-betweens with some more content.To summarize: metal > wood > earth > water > fire > metal and you base the whole setting and story around this.

I like the idea of the "Hero of Prophecy" being killed. It might be even better if he is around doing great things for the first part of the game, and when you cross paths with him for the first time, (maybe 1/6 or 1/5 of the way through the game) something happens (preferably something you caused) and the hero dies in front of your eyes, shattering the hope of everyone around you.

If this were the case, you'd have to run for your life to escape the vengeance of the people you once trusted. Another motivation to travel around might be to try to undo the damage you've done, which would please friends enough to allow them to let you return home.

I really hope that OSARE steers away from cliched or generic plot hooks, especially on plot events that rely solely on the unendingly altruistic attitude of the hero. A deep character is a good character.

Here's my little intro based on the 'cast outs' scenario where a lot of people were murdered due to savage politics reacting to some kind of undeadly faminine that has swept the lands.

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My eyelids, laden by an unfinished sleep, are pierced by fresh sunlight, forcing me to wake.  The buzzing of flies fills my ears as I enter a state of consciousness.  It is loud, nay, defeaning.  The putrid smell of death laces my nostrils as I forcibly inhale, my body starved of air.  I gasp for more as my hands instinctively reach out for something to hold on to, only to find the cold feeling of lifefless flesh filling my palms.  Finally my eyes open to a scene of despair.  As I look around, all I can see is countless dead, under and around me, in a god forsaken pit.  I ask myself, "Where the hell is this?" I chuckle, for Hell might be the appropriate word.

A searing pain strikes deep within my head.  My vision whitens, a hollow noise momentatrily supplants the sound of the flies in my ear drums.  I shake it off.

As I begin to crawl over the lifeless limbs of souls seemingly less lucky than I, more questions begin to fill my mind, as a disturbing trend of the vagueness of my memories becomes apparent.  I remember an execution - but was I the executed or the executioner?  Sliding over bloodied dismembered corpses, I notice that these were not poor people, adorned by fine clothes, though since torn and tarnished and largely stained red.  There are a few hastily made bonfires still smouldering nearby.  Numerous intact items are strewn around the bonfires, as if carelessly tossed.  Whoever did all this was in a hurry and not keen to stick around and finish the job.  Perhaps that is how I survived.  Finally, I reach solid ground.

There it is, that pain again.  Like a blade scything through my skull, causing my legs buckle.  I stumble before dropping to my knees, clasping my head in my hands.  After a deep intake of breath, it subsides.

When I open my eyes again I am staring at the forlorn face of a decapitated victim of this slaughter.  I pause to observe his frozen expression and widened eyes burning with fear.  It is then that the most disturbing realisation occurs.  That I am completely unafraid, despite the severity of my predicament.

The sun is rising and the smell of decay is only going to grow stronger with it.  There must already be beasts tracking the scent through the wilderness.  My instinct or my memory - I can't decide which - tells me there is a village east of here.  I should scavenge what I can and move on.

I think the whole idea of civilization crumbling could be really cool.

If you're gonna go with the corrupted oligarchy then I think it would be really cool if you had sort of a fable element, where the theocrats have been trucking with dark powers for ages to allow for their people to enjoy immortality, presumably from some fell power. Perhaps you could incorporate some of Lamoots ideas, so you have the hero dwelling in the city state of these Theocrats in the Earth region, and they have been laid siege or at war with spirits(elementals?) and men from other kingdoms and regions for decades or centuries, presumably, or at least say the theocrats, to steal the secrets of immortality. These spirits and men attack because the Earth regions theocratic cult is essentially allowing Undead beings from unspeakable hells to feast on the life force of the land in exchange for immortality, only now the effects are really being felt and people from many lands cannot survive, and now even the Earth kingdoms people are falling to undeath because so little life force is left.

You could also have an element where the Mages are beginning to discover the unholy pact the Theocrats have made, and so the undeath is blamed on them and they and their warrior bodyguards are put to death.

Or even more interestingly, maybe the player is a Theocratic Loyalist, young and unaware of the true nature of his religion, who becomes captured transporting the bodies to the outskirts of the city walls, and so believes he must return to his kingdom and regain his standing until he discovers the truth that has been hidden from him.

I think this could fit in nicely with Lamoots ideas about needing to restore the balance of these elements, and start a new cycle. I think it could also provide some very subtle but pleasing social commentary about the woes of not considering the implications of our actions when we overuse our resources.